When an optical fiber cable is laid from a submarine into the water, the cable is usually subjected to tensile stress by the water pressure. In order to prevent the optical fibers of the cable from being unduly stretched by the tensile stress, the optical fiber cable is provided with a core or spacer with a plurality of grooves extending generally in the lengthwise direction of the cable and the optical fibers are loosely fitted in said grooves in the process of manufacturing of the cable so that the optical fibers are not stretched even if the spacer is expanded by the tensile stress due to the water pressure at the time of and after laying of the cable. In the optical fiber cable of the above type, the respective grooves of the spacer are filled up with dampproof or humidityproof mixed articles with the optical fibers without gap for preventing hydrotaxis along the grooves. As the dampproof mixed filler, conventionally powder filler or jelly filler are used. The powder filler serves to prevent the hydrotaxis but can not serve to prevent water immersion. On the other hand, the jelly filler is superior in preventing the water immersion.
However, the way of distribution of the jelly filler in the conventional optical fiber cable shows a disadvantage of causing the optical fibers to be curled locally, which is so called a microbending. More specifically, when the optical fiber cable is subjected to the tensile stress, the optical fibers are strongly stretched with the expansion of the spacer and in turn upon removing the tensile stress, the spacer recovers to its original length. Recovering of the spacer allows the optical fibers to recover to the original loose state. On the contrary, as shown in FIG. 1, the optical fiber 100 can not fully recover due to a large resistance of the jelly filler 101 against the complete recovering of the spacer 103, whereby there occurs a local micro bending 104.
The micro bending of the optical fibers causes decrement of life of the optical fibers due to increment of the bending stress, also it causes increment of the transmission loss.
There are known other types of the optical fiber cable, one of which is filled with grease as the dampproof filler, another of which is provided with a waterproofing plug disclosed in Japanese Patent Publication (unexamined) No. 6206/1981. They can not dissolve the problem of the micro bending of the optical fiber as mentioned above.
Another prior art of the optical fiber cable is disclosed in Japanese Patent Publication (unexamined) No. 62207/1981 in which the optical fibers in the grooves are secured to the spacer with a predetermined interval. The optical cable disclosed in Japanese Patent Publication 62207/1981 is directed to prevent the movement of the optical fibers in the longitudinal direction, therefore in a case where a local tensile stress or deformation is applied to the optical fibers, the optical fibers are excessively expanded or deformed at the local position subjected to the tensile stress since the optical fibers can not be displaced.